Constant force escapement for electric time-pieces



CONSTANT FORCE ESCAPEMENT FOR ELECTRIC TIME-PIECES Filed July 24, 1956 rlnll.

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muw'h m wh United States Patent CONSTANT FORCE ESCAPEMENT FOR ELECTRIC TIME-PIECES F rderic Marti, canton of Neuchatel, and Georges Braunschweig, 165 Rue Numa-Droz, both of La Chauxde-Fonds, Switzerland Filed July 24, 1956, Ser. No. 599,724 Claims priority, application Switzerland May 31, 1956 6 Claims. (Cl. 58-28) This invention relates to a constant force escapement for electric time-pieces such as clocks, travelling-clocks, watches, etc.

According to an important feature of the invention, the escapement comprises a fork which, when acted upon by an impulsing spring periodically recocked by an electric drive member, acts pulsewise upon the balance Wheel, the fork being maintained in the position from which it delivers the pulses by a magnetic force.

As is well known in the clock and watch art, conventional escapements absorb much of the driving power imparted to the balance wheel due to friction which varies considerably with the condition of the lubricant, so that the accuracy with which the balance wheel operates varies itself in the course of time.

It is a main object of this invention to obviate friction in conventional lever escapements and further to suppress lubrication thereof. In the escapement according to the invention, the fact that the fork is maintained in its inoperative positioni.e. the position from which it delivers the pulses-by magnetic means substantially obviates friction, with a resultant accuracy rarely obtained in the electric time-pieces heretofore.

A11 embodiment of the escapement according to the invention is diagrammatically illustrated by way of example in the accompanying drawing, wherein the single figure is a plan view showing merely the elements necessary for an understanding of the invention.

The escapement illustrated in the drawing can be fitted, for instance, to a battery-operated electric small clock or travelling-clock. Referring to the drawing, a conventional balance-wheel 1 with its roller 2, drive pin 3 and hairspring 4, is actuated by a special fork 5 which imparts periodical pulses to the pin 3. The fork 5 is pivotally mounted by means of the pivots on its staff 6 in bearings (not shown). The fork 5 comprises two prongs 7 and 8 of unequal length, the short prong 8 acting merely as a stop for the free end of a flexible strip 9, the other end of which is secured to a projection 10 on the central part or hub of the fork. The arm opposite the prongs 7 and 8 bears a contact stud 11 and, at its end, an iron pin 12. A pulse-initiating or actuating spiral spring 13 has its inward end secured to the fork staff 6 and its outer end secured to a terminal 14 connected to the negative pole of a battery 15.

The armature of an electromagnet 16 is a lever 17 pivoted in a bracket 18 and bearing at its free end a contact stud 19 adapted to co-operate with the contact stud 11 of the fork 5. A return spring 20- tends to main tain the contact studs 19 and 11 apart from one another. The electromagnet 16 is connected to a terminal 21 connected to the positive pole of the battery 15. The lever 17 can oscillate between two stops 22 and 23.

A small permanent magnet is adapted to attract the iron pin 12 of the fork 5, and a fixed stop 25 determines the inoperative position of the fork 5.

The device hereinbefore described operates as follows:

The fork 5 is constantly urged by the actuating spiral spring 13, previously cocked, so as to keep the balancewheel 1 oscillating at a steady amplitude. The actuating spiral 13 is periodically recocked by the electromagnet 16, the armature 17 of which is attracted when the circuit is closed through the members 15, 14, 13, 6, 11, 19, 20, 16, 21. As it is thus attracted, the armature contact stud 19 co-operates with the fork stud 11 to repel the fork 5, to the staff 6 of which is secured the inner end of the actuating spiral spring 13.

The fork 5, when in the inoperative position illustrated in solid lines, bears against the fixed stop 25 and is maintained in that position by the permanent magnet 24 which attracts the soft iron pin 12 with a force slightly greater than the force of the actuating spiral spring 13.

When, during onehalf of a balance-wheel oscillation, the pin 3 moves in the direction F between the prong 7 and the resilient strip 9 of the fork 5, the said pin 3 pulls the fork away from the magnet 24, the attractive force of which decreases rapidly as the pin 12 moves away. The actuating spiral spring 13 then acts upon the fork 5 which, by way of its prong 7, imparts a pulse in the direction F to the pin 3 of the balance-wheel 1, such pulse being powerful enough to maintain balancewheel oscillation. At the end of the travel resulting from the pulse (position shown in dot-and-dash lines), the pin 3 separates from the fork, the contact stud 11 of which stops against the stud 19 of the electromagnet armature 17 and thus closes the energising circuit thereof. The armature is thus immediately attracted by the electromagnet and repels the fork 5 in the opposite direction F until the fork is very near its inoperative position, that is far enough for the permanent magnet 24 acting upon the pin 12 to overcome the torque of the actuating spiral spring 13 and to return the fork against the fixed stop 25 which defines its initial or inoperative position.

The armature 17 is retained by the stop 23 being so adjusted that the electric circuit is broken before the fork reaches its inoperative position, that is, at the very instant when the permanent magnet 24 begins to act upon the pin 12. The armature 17 is then returned to its initial position by the return spring 20. During this time, the balance-wheel 1 executes one-half of an oscillation, and when the pin 3 rotating in the direction F returns to the operative region of the fork 5, it abuts from the right the end of the flexible strip 9 which extends from the end of the short prong 8. The strip 9 yields to the force exerted by the pin 3 and allows the same to pass. Half an oscillation later, the pin 3 returning in the direction F again reaches the entry of the fork and abuts the strip 9 from the left. The strip 9, however, cannot now yield since it bears against the inner surface of the short prong 8. The fork 5 is thus urged in the direction F and the cycle begins again with another pulse in the direction F initiated by the actuating spiral spring 13.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions, and, accordingly, it is desired to cornprehend such modifications within this invention as may fall within the scope of the appended claims.

What we claim is:

1. In an electric time-piece having a balance wheel, a constant force escapement comprising a pivotally mounted fork for pulsing the balance wheel, an impulse spring acting upon said fork, an electric drive member for periodically recocking said spring, and magnetic means for maintaining said fork in the position from which it delivers the pulses.

2. In an electric time-piece having a balance wheel, a constant force escapement as claimed in claim 1 with said fork having prongs on one end thereof for pulsing said balance wheel and an iron pin on the other end of said fork adapted to be attracted by said magnetic means to retain the fork in the inoperative position against a fixed stop after each pulse. g

3. In an electric time-piece having a balance Wheel, a constant force escapement as claimed in claim 1 wherein said balance wheel has a driving pin thereon and said fork has two prongs of unequal length and a flexible strip, the end of said flexible strip extending from the short prong and bearing against the inner surface thereof so as to allow said driving pin on the balance wheel to escape in one direction only.

4. In an electric time-piece having a balance wheel, a constant force escapement comprising a pivot staii, a fork pivotally mounted upon said pivot staff for pulsing said balance Wheel, a spiral impulsing spring disposed around said pivot staff with the inner end of said spring being secured to said staff while the outer end thereof is connected to a source of electric current, an electric drive member for periodically recocking said spring, magnetic means for maintaining said fork in the position from which it delivers the pulses, the magnetic force exerted by said magnetic means being greater than the force exerted by said spring, said magnetic force for maintaining the fork in position being independent of the electrical circuit energizing said electric drive member for periodically recocking said spring.

5. In an improved time-piece having great accuracy and efiiciency, a mechanically oscillatable member, an impulse member, spring means biasing said impulse member in one direction, magnetic latch means for holding said impulse member in cocked condition against the action of said spring means, said oscillatable member being adapted periodically to engage said impulse memher and un-latch it to receive an impulse of energy stored in said spring means, and drive means for periodically re-cocking said impulse member against the action of said spring means.

6 A highly accurate time-piece which can operate for a great length of time from a small battery or the like, said time-piece including'an oscillatable balance wheel having a pallet pin, a pivoted drive lever having one end engageable by said pallet pin, a hairspring biasing said lever in one direction'frictionless latch means for holding said lever in cocked condition against the action of said hairspring, said pallet pin on each oscillation'of said balance wheel contacting said end of said lever to unlatch it and to receive from it an impulse of force, and drive means for periodically re-cocking said lever against the action of said hair'spring.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,516 Minneker Mar. 14, 1939 FOREIGN PATENTS 667,885 Great. Britain -a Mar. 12, 1952 

